1. Field of the Invention
This invention relates to a convenient copying apparatus which can fully function both as a sheet original copying apparatus and a thick original copying apparatus and which is capable of increasing the copying speed in accordance with the copy size and incorporates various devices for convenient use.
2. Description of the Prior Art
Copying machines have heretofore been classified into two types, namely, those for copying sheet originals exclusively and those capable of copying books or other three-dimensional originals.
The copying machines exclusively for sheet originals cannot copy books or other thick originals but they can produce copies of sheet originals simply by inserting sheet originals into an inlet port and for one and the same process, these machines involve no copying stroke of the original carriage or the optical system and can correspondingly increase the copying speed (by approximately 2 times). Further, the mechanical constructions are simple and this leads to economical advantages of the machines. Also, the copying machines of this type readily permit inclusion of autofeeder devices for originals.
In contrast, the copying machines capable of producing copies of books or other thick originals have a great advantage that they can copy sheet originals as well as books or like originals, but inasmuch as these machines are designed such that any original to be copied must be flatly spread over the original carriage, a sheet original as well as a thick original has to be placed on the glass plate of the original carriage by manually raising an original keep cover and then closing the cover, whereafter a copy button must be depressed to effect copying. Further, the original carriage or the optical system in these machines has the copying stroke, which means a corresponding loss of time, and thus the copying speed is necessarily reduced for one and the same process. Moreover, complicated mechanical constructions lead to higher cost of the machines. Further, it is very difficult to provide these machines with autofeeder devices for originals.
For the reasons set forth above,, the two types of copying machines enjoy their own markets.
In most offices, however, demand concentrates on copies of sheet originals rather than copies of thick originals. Therefore, users have been compelled to purchase more expensive thick original copying machines at the sacrifice of the expediency of the sheet original copying machines. To overcome such inconsistency, there have been devised some copying machines which retain the features of sheet original copying machines and are stil capable of copying thick originals as well. These include the following types:
I. The type wherein the portion of the machine which is above the passage surface for a sheet original is removable, and when copies are to be made of a thick original, such portion is removed to expose the sheet original transport rolls in the machine body so that the thick original is manually urged against the rubber rolls, which transport the thick original for slit exposure; and
II. The type which is similar in construction to the type I, with the exception that a carrier comprising a transparent plate of glass, plastics or like material is prepared on which a thick original may be placed and two or more pairs of transport rolls hold therebetween the ends of the carrier to transport the carrier for exposure.
Since these machines differ very little in mechanical construction from the sheet original copying machines, they are not so expensive, although they suffer disadvantages as follows:
1. On the part of users, it is considerably cumbersome to remove a portion of the machine and a limited office space would offer a problem of finding a space for the removed portion. Further, the method II above would offer problems in storing the carrier. PA1 2. In the method I above, a great load variation would occur with respect to the machine body depending on the manner in which the original is urged, and in the method II above, the thickness of the carrier would cause a corresponding variation in the length of the optical path, which would result in improper focusing and accordingly a corresponding error of periodic speed, thus greatly aggravating the quality of resultant copy images. PA1 3. A gear and sprocket wheel arrangement for driving the original transport rolls at the end thereof, and in the method II, the carrier transport rolls, are projected upwardly beyond the original transport surface and such surface cannot be made flat, thus making it impossible to copy a part of a large-sized original. PA1 4. Where the original to be copied is a book or the like having a substantial thickness and having the leading edge thereof (as viewed in the direction of transport) complicatedly configured (due to the presence of a book cover or the inclined edge surface resulting from the opened position of the book), an edge detector switch for detecting the leading edge of sheet original is used to detect the leading edge of the book and this results in appreciable irregularities of the leading edge position in the resultant copies. PA1 1. It is difficult to insert a sheet original of large size into the sheet original inlet port because the insertion of sheet original must be done horizontally; and PA1 2. The movable original carriage is so heavy that smooth reciprocation thereof is difficult.
Thus, the above-mentioned types of machines are hardly available for practical use and the above-noted features could only be the sales points, at best.
It will thus be noted that these conventional copying machines cannot be said to be completely practical. However, as an improvement over the prior art, the following system has been proposed and successfully put into practice.
According to this system, an electrophotographic copying machine of the movable carriage and slit exposure type is constructed such that a movable original carriage and a sheet original transport portion comprising two or more pairs of rolls have their exposure surfaces in the same plane and the original carriage and the sheet original transport portion are integral. To produce copies of a sheet original, the original may be inserted into the sheet original transport portion and thereby moved to an illuminating portion. When copies of a book or other thick original are to be produced, this system is highly useful because it has overcome the above-noted various disadvantages. However, application of such system to the copying machines for the production of large-sized copies would encounter the following operational and technical problems:
With regard to developing device, liquid development is superior to dry development in that it is higher in developing efficiency and can provide better image reproduction. On the other hand, liquid development is delicate in developing action and therefore, cumbersome procedures are required in construction of the portion in which the photosensitive medium is contacted by developing liquid, and maintenance of the toner density of the liquid and the circulation system therefor as well as periodic servicing or inspection is imperative.
Particularly, the developing electrode portion is provided with various mechanisms for ensuring production of good copies, such as a scraper for removing stains on that side of transfer paper adjacent the separator belt and a fog removing roller for removing any fog from the transfer paper, and these mechanisms require periodic servicing or inspection and would sometimes require replacement of parts, disassembly and/or cleaning.
Further, if the width of transfer paper is increased, the width of the developing electrode will also have to be increased and this will unavoidably lead to an increased size of the developer container on which the developing electrode is mounted.
The increased size of the developer container means a correspondingly increased quantity of developing liquid therein, which would prevent sufficient agitation of the developing liquid, thus reducing the frictional charging efficiency of toner and carrier in the developing liquid.
If powerful agitation is effected to enhance the agitating efficiency, the agitation will increase the temperature of the developing liquid to thereby increase the amount of developing liquid consumed due to natural evaporation of the liquid.
When copying operation is started after a long down-time, liquid agitation cannot sufficiently be achieved in a short time, as a result of which the first several copies would be low in contrast. Also, the developing device itself would become larger than size A2 (420 .times. 594mm) and accordingly heavier in weight and therefore, if the developer container and the developing electrode were constructed integrally with each other as described, the developing device would become inconvenient to take in and out of the machine body and difficult to service and inspect.
During down-time of the machine, developing liquid tends to evaporate and toner in the carrier liquid readily solidifies into toner masses, which may mix with the circulating developing liquid and be supplied to the developing electrode portion to create unevenness of the resultant copy images or injure the photosensitive medium.
Also, in the electrophotographic art using liquid developer to develop electrostatic latent image, there has heretofore been a developing device which comprises a developer containing portion for containing the developer therein and a developing portion for developing an object to be developed on a photosensitive medium or the like, the developer containing portion and the developing portion being individually constructed with a distance therebetween. In such device, the developing portion and the developer containing portion have been connected together by pipes or other connecting means so that the developer may be supplied from the containing portion to the developing portion and collected from the latter into the former portion. For the purposes of maintenance, repairs, inspection or the like, removal of the developer containing portion or the developing portion must be done either by excepting the connecting pipes or by simultaneously removing the two portions unstably connected by the thin pipes. In the first-named case, one end of the excepted pipes would interfere with the removal of the portion to be removed, and developer would even leak through the disconnected pipe end to contaminate the device. In the latter case, simultaneous removal of the two portions connected by the thin pipes is a difficult task and, even if only one of the two portions is to be removed, both portions need be removed and this is wasteful and time-consuming work.
For the detection of the density of the developing liquid in the developing device of the copying machine, use has been made of photoelectric detector means which comprises a light source or lamp and a light-sensing element. However, such photoelectric detector means simply immersed in the developing liquid may often have its detecting function reduced by toner which tends to precipitate and solidify to stick to a wall portion corresponding to the optical path of the photoelectric detector means. In another prior art arrangement wherein the photoelectric detector means is disposed outside the developer container and supply of developing liquid is effected by pumping means, when the copying machine has been stopped from operating, developing liquid rarely stays in the detector means so that the surface of a transparent member accommodating therein the light source and light-sensing element is dried to permit residual toner to stick to said surface, thus rendering accurate detection of the density of developing liquid impossible.
In the drying-fixing device of copying machine, a heat source commonly used is a heating plate which comprises a plate-like nichrome wire would around a flat mica plate and having the opposite surfaces covered with layers of mica for insulation, the heating plate being urged against a metal plate of good heat conductivity to heat the metal plate. Since, however, the mica as the insulating material is hard, it is difficult to bring such material into intimate contact with the heating plate and this is particularly so when the heating plate has a complicatedly curved surface configuration. Therefore, poor heat transfer may occur in the areas of non-contact between the plate-like heater and the heating plate and the portion of the nichrome wire in such areas may often be overheated and broken. Further, unless the heating plate directly contacted by copy medium, for example, paper, has a curved surface designed well in view of the properties of the paper when heated and the configurations of the passages before and after the heating plate, the contact between the paper and the heating plate would be worse to reduce the heat transfer efficiency therebetween.
In the conventionally used heating plate type heater structure which comprises a convex-surfaced heating plate, a plate-like heater and a support plate having a convex surface similar to that of the heating plate and wherein the heater is brought into intimate contact with the heating plate by bolting it to a bottom plate integral with the heating plate, the simple convex configuration of the heating plate permits the plate-like heater to be well brought into intimate contact with the heating plate by adjusting the fastening force of screws in use. However, if the screws are tightened too much, the heating plate will be deformed or the support plate will be deformed by the repulsion of the plate-like heater, thus adversely affecting the contact and causing the above-noted disadvantages. If the thickness of the heating plate and of the support plate is increased to prevent the deformations thereof, their heat capacities will be increased to increase the time required for them to attain a predetermined temperature. Thus, the heater structure now under discussion is hardly applicable to the heat plate having surfaces concavely and convexly curved in accordance with the properties of paper and with the configurations of the passages before and after the heating plate.
Further, in the development process of the wet type electrophotographic copying machines, solution of hydrocarbon is used as carrier and some amount of such solution remains on the surface of copy paper onto which a toner image has just been transferred from the photosensitive drum. In the drying-fixing devices of the type which fixes the toner image on the copy paper while evaporating the residual hydrocarbon, it is required that the heat from the heat source be efficiently transferred to the copy paper.
Such drying-fixing devices include: (a) those which use infrared ray lamps; (b) those which utilize a blast of hot wind; and (c) those which employ heating plates. Type (a) suffers from disadvantages resulting from heat scattering, temperature rise in the machine and adverse effect of infrared rays on the image transfer device. Type (b) is low in drying efficiency and requires the copy paper transport passage in the drying-fixing device to be longer, which in turn leads to a large size of the device.
Type (c) is such that the heating plate is heated to about 230.degree.C by a heater and copy paper is advanced over the heating plate with the back side thereof in contact therewith for drying and fixing, and if a good contact is provided between the heating plate and the copy paper the device of this type may be small in size and light in weight to accomplish the drying and fixing with a very high efficiency.
Nevertheless, the properties of copy paper which will be warped when heated make it very difficult for such copy paper to advance while maintaining a good contact with the heating plate, and there is another problem that the distance of transport on the heating plate cannot be so long because of the requirement for reduced size of the device.
Also, in copying machines, special attention is paid to the design thereof so as to prevent jamming of copy paper in the interior of the machine, but should jamming occur, removal of the jammed paper must and can be done with ease. For this purpose, it has heretofore been practised to provide the copy paper transport passage by divided surfaces to thereby permit the copy paper transport portion to be divisibly constructed.
However, various factors may cause copy paper to be jammed as it is transported in a narrow passage. Thus, a design for reducing the frequency of jamming is necessary and at the same time, a construction is necessary which will readily permit removal of jammed paper whenever it occurs.
Further, the copy paper feeder bed of copying machine has heretofore been designed such that it can carry thereon and supply therefrom a plurality of sizes, including a maximum size and lesser sizes, of copy mediums in accordance with the performance of the machine.
However, when one side plate of the paper feeder bed is displaced to match a small size of copy paper, the distance between springs and paper feed roll which produce paper feeding forces differs from one side to the other side of the feeder bed, and this in turn leads to different pressure contact forces and accordingly different feeding forces on the opposite sides, with a result that copy paper is fed obliquely.
Also, confirmation of the sizes of copy paper carried on the feeder bed must be directly done by manually opening a lid such as outer plate or the like.